New wave of malicious XLS files spreading Zloader


The SonicWall Capture Labs Threat Research Team has observed a new wave of malicious Excel files distributing Zloader.

From the onset of 2020, we have observed malware campaigns using the Macro 4 feature available in Microsoft Excel, which we have written about in our previous blog posts.

Thus far, malicious Excel files used for spreading Zloader have contained  the following characteristics:

  • Two Sheets: Some of them had one visible sheet  and one other sheet hidden whereas in others both the sheets are visible
  • Auto_Open name is not visible in the Name Manager dialog box; and
  • Excel in-built functions CHAR or MID were used to operate upon cell data which were later joined using concatenation operator ‘&’ to construct further instructions

Fig-1: Excel file used earlier by Zloader

Transformations observed in this new wave of MS-Excel files :

  • Excel has more than 2 sheets with one visible worksheet and remaining sheets, including a macro sheet, are hidden
  • Auto_Open is visible in the name manager dialog box;
  • Data is simply retrieved from cells, joined using a concatenation operator to construct further instructions; and

This re-modelling gives the file a more legitimate appearance.

Fig-2: Excel with visible and hidden sheets

Fig-3: Auto_Open name visible in Name Manager dialog box


Fig-4: Plain cell data reading and concatenation


These files were created either on 3rd or 4th June 2020 which indicates the freshness of samples and RTDMI detection effectiveness.


Fig-5: RTDMI Detection

Indicators Of Compromise:

SHA256 of Malicious MS-Excel files:

  • 41879c115ae2a85d0a136d62b6169e95756f0b9bd8f47e32238a4e2e26e0fc03
  • 5c264ad2647000a4e260ff5f60df04a2d9b24676dc7b4bc45e07e1b70c053b0c
  • cffef738b2ec86d56432f0a988cf4a8511bf813515edc91b2e1d6729d5f1cfef
  • 0c47d7fe4c8d6563fd4c616080703a974d04694658b23c2d36ecc03b03eeec32
  • b24019b7b02989bb5e02e5243d704d63bab71442613574a7d4a3a69a8b36541e
  • 9c1d837a523f86c8117be3a607f1910e248993e6e77c47bb86b17eec2503e627
  • 56a662fcfaa103edd1fc45ed24c7e974662136a95c2191e65f46702b4d98a7ea
  • 0e186d534befcd860e2618d4cf77af6180effe42b07cecde75164142e2090ff4
  • 2a0d637ff6bcdf1fd37905fb84926e7ef35190fc62e97f3305b1da65b9f15a8f
  • f83f7117ddab2be46f57000e3623a22f15f46da2c4878000bb8de87c9b2ebba9

Network Connectivity:

  • https://destgrena[.]at/3/tsk.dll

SHA256 of payload:

  • 444a977a2d0768f115fef0704a3f067d937823877a8202a4796425a58f49b6e0
  • 1526e62be6b34c6ea39220569f90e44cf04efccaa4b4ed75af8a4f669f10b2e9
  • 06a297b1c6b0b25ef3cc3ca6c77ad62e2ff5bd801c8cb9c081fbb4ea90d313fa
  • 363d8b43541e37ae9b25a5fd6b6eef5245fc667c449b3d37e45a3de15d60780b
  • 6c95e2eeeb98b0557a849e972ad26d2c77e7d9d8bfbd45ec680cfb6eb508667c
  • 8cbe7c61e8b1bd3d2187b9e7f10449dfcb4f20c309cf768433f164dc83149a1a
  • 327b41d9bcad614f2e62b3e838ae9a1237dc0bd3ed17c59e1290abf596e5f178
  • b22779f52daffae57465b8becfa4e19240304d6e835ffe4448fa4d5588a2e9cc
  • e27bcec6ccb48108abdf87328d0e260de1036df851af20317061da2419734d1f


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The SonicWall Capture Labs Threat Research Team gathers, analyzes and vets cross-vector threat information from the SonicWall Capture Threat network, consisting of global devices and resources, including more than 1 million security sensors in nearly 200 countries and territories. The research team identifies, analyzes, and mitigates critical vulnerabilities and malware daily through in-depth research, which drives protection for all SonicWall customers. In addition to safeguarding networks globally, the research team supports the larger threat intelligence community by releasing weekly deep technical analyses of the most critical threats to small businesses, providing critical knowledge that defenders need to protect their networks.